In the cyclic fatigue testing of the mechanical strength of samples such as ceramic or the like there is known a three point bending test apparatus in which one surface of the sample to be tested is supported at two points thereof, the other surface is supported at the center portion thereof and a bending fatigue of the sample is measured by applying a dynamic load on the either side thereof. An apparatus generally used for such fatigue testing typically comprises a linear reciprocating mechanical actuator mechanism such as a piston and a cylinder as an impact source for applying the dynamic load on the either side of the sample.
U.S. Pat. No. 4,572,011 discloses such a linear reciprocating mechanical actuator mechanism comprising a hydraulic actuator and a servo mechanism.
With the known testing apparatuses, it is complicated to control or adjust a driving force to be applied to the sample being tested so that the intended accuracy in determining the load can be attained. Also, the conventional cyclic fatigue testing apparatus have disadvantages that they can not generate a high frequency driving force, the operation of them is noisy, and there may easily occur an abrasion or wear due to a mechanical friction, leading to make it difficult to maintain the test conditions constant during the test procedure.
Further, the problem arises in the known apparatuses that it is difficult to operate them with sufficient accuracy and thus it may result in that the test sample is exposed to harmful overloads which influence the fracture behaviour and the measured results in a non-acceptable way.
Furthermore, with the conventional system using a magnetic or hydraulic actuator which has a speed of response of the order of mm sec, it is impossible to generate a vibration having a high frequency cycle of 100 Hz or more.
Therefore, an object of the present invention is to provide a cyclic fatigue testing apparatus intended for testing the cyclic fatigue of samples such as ceramic or the like, which can eliminate the above-mentioned disadvantages.
It is a further object of the present invention to provide a cyclic fatigue testing apparatus conveniently used for test samples having very low strength.